Lung cancer is the leading cause of cancer deaths in both men and women in the United States, with over 155,000 patients dying each year in this country alone. Several factors contribute to the poor outcome of lung cancer patients, but, as in most solid tumors, the ability of cancer cells to leave the primary tumor and establish inoperable metastases is a major impediment to successful therapy. Metastasis thus represents a major clinical challenge that is driven by as yet poorly understood cell state alterations. By integratin gene expression analyses on murine models of metastatic lung adenocarcinoma and human lung adenocarcinomas we identified the transcription factor Arntl2 as a key driver of lung adenocarcinoma metastatic ability. Arntl2 appears to drive metastatic fitness by controlling the expression of a complex pro-metastatic secretome that has the ability to greatly increase clonal growth potential. In Aim1, we will functionally interrogate Arntl2 function in human and mouse lung adenocarcinoma cell lines. We will perform gain- and loss-of-function experiments and fully assess the cellular phenotypes driven by Arntl2. Transplantation assays and quantification of initial adhesion, proliferation, and cell death within the metastatic site in vivo will elucidate te cellular consequence of high Arntl2 expression. In Aim2, we will investigate which Arntl2-regulated secreted factors cooperate to drive clonal growth and metastatic ability. We will integrate screening of recombinant proteins in cell culture, gain- and loss-of-function experiments in cell culture and in vivo, and therapeutically target pathways downstream of key pro-metastatic secreted proteins to better understand the importance of autocrine metastatic niche factors. In Aim3, we will use novel methods for CRISPR/Cas9-mediated genome editing and lentiviral-mediated cDNA expression to test the requirement and sufficiency of Arntl2 and Arntl2- regulated genes to promote step of the metastatic cascade in autochthonous mouse models of human lung cancer. Given the immense clinical impact of metastatic cancer and the current gap in understanding the molecular underpinnings of this disease state, both clinical practice and patient outcome would be greatly impacted by any new therapies that might result from the fundamental knowledge gained from our proposed analyses. By combining quantitative methods and powerful in vivo methods, we hope to uncover general principles that govern tumor progression and metastatic spread and ultimately reveal novel therapeutic targets across the continuum of cancer progression.